From: Tom MacIntyre
Subject: Re: Which basic compiler to buy?
References: <email@example.com> <firstname.lastname@example.org> <email@example.com> <3E036EE0.DE68AFD7@sbcglobal.net>
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Date: Sat, 21 Dec 2002 00:08:37 GMT
NNTP-Posting-Date: Fri, 20 Dec 2002 20:08:37 AST
On Fri, 20 Dec 2002 13:26:24 -0600, gary drummond
>Tom Del Rosso wrote:
>> "Tom MacIntyre" wrote in
>> message news:firstname.lastname@example.org...
>> > >
>> > >To be fair, IBM's hardware set the memory limit.
>> > >
>> > But wasn't DOS still incapable of exceeding the 640k long after the
>> > hardware support was there?
>> That was mostly because of Intel's hardware goof. Their segmented
>> memory made it necessary for any program of more than 64k to do a lot of
>> address arithmetic, and that made it hard to migrate to a different
>> system with more segments. DOS couldn't really have been designed with
>> enough foresight to have been portable to the 286 memory model. Intel's
>> data on the 8086 didn't say a word about planning for the segments
>> becoming virtual, so the natural assumption was that consecutively
>> numbered segments were consecutive. In fact Intel encouraged that
>> assumption when they explicitly stated that segments and offsets could
>> be added different ways, for example the way 0040:017A = 0000:057A.
>> Getting back to IBM's goofs, the original DOS made by a small company
>> which sold it to MS, had 1 meg of RAM, because they used a little 8086
>> system that could switch out the ROM! I don't know who made that
>I think it was an 8088 at first...
Memory may let me down again, but the 8086 was first, and they cut it
back on the external bus in the 8088. Anyone?